Who this is for
This page is for people with hormone receptor–positive early breast cancer who are approaching five years of hormone therapy and are unsure whether they should continue treatment beyond that point.
Reaching the five-year mark can feel like a milestone. Many patients expect to stop treatment and move forward. Being told that therapy might continue for another five years can feel exhausting — especially if side effects have been significant. The key question becomes: does extending treatment meaningfully reduce your risk, or are you continuing without clear benefit?
Why this question matters
Hormone receptor–positive breast cancer has a unique pattern.
Unlike some other subtypes, the risk of recurrence does not disappear after five years. Late recurrences can occur, particularly in patients with higher-risk biology.
Historically, many patients were advised to continue endocrine therapy for up to ten years based on overall recurrence reduction seen in large trials.
However, the benefit is not uniform for everyone.
This is where the Breast Cancer Index (BCI) test becomes relevant.
What is the Breast Cancer Index (BCI)?
BCI is a genomic test performed on stored tumour tissue removed at the time of surgery.
It is not a clinical risk calculator.
It is a laboratory-based genomic assay. The BCI is currently validated for patients with 0 to 3 positive nodes
BCI provides two types of information:
• Prognostic information about risk of late recurrence (years 5–10)
• Predictive information about likelihood of benefit from extended endocrine therapy
This distinction is important.
It does not simply estimate risk.
It attempts to identify who is likely to benefit from continuing therapy.
Key evidence supporting extended endocrine therapy and BCI
• Extended endocrine therapy in broad populations reduces recurrence risk by approximately 2–5% in absolute terms over years 5–10.
• Studies evaluating BCI have shown that patients classified as “BCI high” derive meaningful benefit from extended therapy, while “BCI low” patients show little or no additional benefit.
• In validation cohorts, BCI demonstrated predictive ability for extended therapy benefit with statistically significant interaction between risk category and treatment effect.
What this means
Extended hormone therapy does reduce recurrence in some patients — but not all.
BCI helps refine this decision by identifying a subgroup where continued therapy is likely to be worthwhile, and another where additional years may provide limited benefit.
It shifts the conversation from “everyone should continue” to “who benefits most?”
Why this matters in Melbourne and Australia
In Australian practice, extended endocrine therapy is commonly discussed at the five-year mark for hormone receptor–positive early breast cancer.
BCI is a separate paid genomic test performed on tumour tissue. It is not routinely covered under all funding pathways.
In Melbourne clinical practice, the decision to order BCI often depends on:
• Initial tumour size and nodal status
• Patient age
• Tolerance of hormone therapy
• Anxiety regarding recurrence
• Willingness to continue treatment
The test is most useful when the decision is uncertain — not when risk is clearly very low or very high.
Side effects and quality of life
Extended endocrine therapy can be associated with:
• Joint pain
• Hot flushes
• Bone density loss
• Mood changes
• Sexual health concerns
For some patients, these are manageable.
For others, they significantly affect quality of life.
The decision to extend therapy must balance recurrence risk reduction against daily wellbeing.
Precision matters here.
Side effects and quality of life
Extended endocrine therapy can be associated with:
• Joint pain
• Hot flushes
• Bone density loss
• Mood changes
• Sexual health concerns
For some patients, these are manageable.
For others, they significantly affect quality of life.
The decision to extend therapy must balance recurrence risk reduction against daily wellbeing.
Precision matters here.
How BCI fits into modern breast cancer care
The broader shift in oncology is toward risk-adapted therapy.
TAILORx helped reduce unnecessary chemotherapy.
RxPONDER refined treatment in node-positive disease.
BCI helps refine duration of endocrine therapy.
The theme is consistent:
More treatment where benefit is proven.
Less treatment where benefit is minimal.
Key Takeaway
• Not all patients benefit equally from extending hormone therapy beyond five years.
• The Breast Cancer Index (BCI) helps identify who is likely to benefit from continued treatment.
• The decision should balance recurrence risk reduction with quality of life.